U.S. patent number 5,682,312 [Application Number 08/618,079] was granted by the patent office on 1997-10-28 for self-adapting excavation control system and method.
This patent grant is currently assigned to Caterpillar Inc.. Invention is credited to David J. Rocke.
United States Patent |
5,682,312 |
Rocke |
October 28, 1997 |
Self-adapting excavation control system and method
Abstract
A control system for automatically controlling a work implement
of an excavating machine through a machine work cycle in disclosed.
The work implement including a boom, stick and bucket, each being
controllably actuated by at least one respective hydraulic
cylinder. A plurality of command signal magnitudes associated with
at least one hydraulic cylinder are stored. The command signal
magnitudes are represented by a plurality of control curves, where
each control curve is responsive to a material condition setting
that is representative of a predetermined condition of the
excavating material. A microprocessor selects one of the plurality
of control curves and responsively produces a command signal having
a magnitude dictated by the selected control curve. A
electrohydraulic system receives the command signal and
controllably actuates predetermined ones of the hydraulic cylinders
to perform the work cycle.
Inventors: |
Rocke; David J. (Eureka,
IL) |
Assignee: |
Caterpillar Inc. (Peoria,
IL)
|
Family
ID: |
22809414 |
Appl.
No.: |
08/618,079 |
Filed: |
March 18, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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217033 |
Mar 23, 1994 |
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Current U.S.
Class: |
701/50;
37/414 |
Current CPC
Class: |
E02F
3/437 (20130101); E02F 3/439 (20130101) |
Current International
Class: |
E02F
3/43 (20060101); E02F 3/42 (20060101); G06F
019/00 () |
Field of
Search: |
;364/167.01,181,424.07
;37/414,416 ;172/4.5 ;414/699 ;395/904 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Design of Automated Loading Buckets", P. A. Mikhirev, pp. 292-298,
Institute of Mining, Siberian Branch of the Academy of Sciences of
the USSR, Nevosibirsk. Translated from Fiziko-Tekhnicheskie
Problemy Razrabotki Poleznykh Iskopaemykh, No. 4, pp. 79-86,
Jul.-Aug., 1986. Original Article Submitted Sep. 28, 1984, Plenum
Publishing Corporation, 1987. .
"Method of Dipper Filling Control for a Loading-Transporting
Machine Excavating Ore in Hazardous Locations", V. L. Konyukh et
al., pp. 132-138, Institute of Coal, Academy of Sciences of the
USSR, Siberian Branch, Kemorovo. Translated from
Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No.
2, pp. 67-73, Mar.-Apr., 1988. .
"Automated Excavator Study", James G. Cruz, A Special Research
Problem Presented to the Faculty of the Construction Engineering
and Management Program, Purdue University, Jul. 23, 1990. .
"Just Weigh It and See", Mike Woof, p. 27, Construction News, Sep.
9, 1993. .
"An Intelligent Task Control System for Dynamic Mining
Environments", Paul J.A. Lever et al., pp. 1-6, Presented at 1994
SME Annual Meeting, Albuquerque, New Mexico, Feb. 14-17, 1994.
.
"Cognitive Force Control of Excavators", P.K. Vaha et al., pp.
159-166. The Manuscript for this Paper was Submitted for Review and
Possible Publication on Oct. 9, 1990. This Paper is Part of the
Journal of Aerospace Engineering, vol. 6, No. 2, Apr. 1993. .
"A Laboratory Study of Force-Cognitive Excavation", D.M. Bullock et
al, Jun. 6-8, 1989, Proceedings of the Sixth International
Symposium on Automation and Robotics in Construction. .
"A Microcomputer-Based Agricultural Digger Control System", E.R.I.
Deane et al., Dec. 20, 1988, Computers and Electronics in
Agriculture (1989), Elsevier Science Publishers. .
"Artificial Intelligence in the Control and Operation of
Construction Plant-The Autonomous Robot Excavator", D.A. Bradley et
al., Automation in Construction 2 (1993), Elsevier Science
Publishers B.V. .
"Control and Operational Strategies for Automatic Excavation" D.A.
Bradley et al., Proceedings of the Sixth International Symposium on
Automation and Robotics in Construction, Jun. 6-8, 1989. .
"Development of Unmanned Wheel Loader System-Application to Asphalt
Mixing Plant", H. Oshima et al., Published by Komatsu, Nov. 1992.
.
"Motion and Path Control for Robotic Excavation", L.E. Bernold,
Sep. 1990, Submitted to the ASCE Journal of Aerospace
Engrg..
|
Primary Examiner: Park; Collin W.
Attorney, Agent or Firm: Kibby; Steven G. Masterson; David
M.
Parent Case Text
This is a file wrapper continuation of application Ser. No.
08/217,033, filed Mar. 23, 1994, now abandoned.
Claims
I claim:
1. A control system for automatically controlling a work implement
of an excavating machine through a machine work cycle, the work
implement including a boom, stick and bucket, each being
controllably actuated by at least one respective hydraulic
cylinder, the hydraulic cylinders containing pressurized hydraulic
fluid, the control system comprising:
memory means for storing a plurality of command signal magnitudes
for controlling at least one hydraulic cylinder, the command signal
magnitudes being represented by a plurality of control curves, each
control curve corresponding to a material condition setting that is
representative of a condition of an excavated material;
logic means for selecting one of the plurality of control curves
responsive to a determined said material condition setting
indicated by the condition of the excavated material and producing
command signals having a magnitude dictated by the selected said
control curve; and
actuating means for receiving the command signals and responsively
actuating predetermined ones of the hydraulic cylinders to perform
the work cycle.
2. A control system, as set forth in claim 1, wherein said logic
means determines the condition of material excavated during a work
cycle and automatically selects said one of the plurality of
control curves, said logic means producing said command signals
from said selected control curve during a subsequent work cycle in
response to the determined material condition setting.
3. A control system, as set forth in claim 2, including an operator
interface means for providing the operator an option of manually
selecting one of the plurality of control curves.
4. A control system, as set forth in claim 1, wherein said logic
means produces said command signals having magnitudes dictated by
said selected control curve responsive to a force imposed on a said
hydraulic cylinder.
5. A control system, as set forth in claim 4, further comprising
hydraulic fluid pressure sensors for measuring said force imposed
on said hydraulic cylinder.
6. A method for automatically controlling a work implement of an
excavating machine through a machine work cycle, the work implement
including a boom, stick and bucket, each being controllably
actuated by at least one respective hydraulic cylinder, the
hydraulic cylinders containing pressurized hydraulic fluid, the
method comprising the steps of:
storing a plurality of command signal magnitudes associated with at
least one hydraulic cylinder, the command signal magnitudes being
represented by a plurality of control curves, each control curve
corresponding to a material condition setting that is
representative of a condition of an excavated material;
selecting one of the plurality of control curves responsive to a
material condition setting determined from said excavated material
condition and producing a command signal having a magnitude
dictated by the selected control curve, responsive to a force
imposed on a said hydraulic cylinder;
receiving the command signal and controllably actuating
predetermined ones of the hydraulic cylinders in response to said
command signal to perform the work cycle.
7. A method, as set forth in claim 6, further including the step of
determining said material condition setting based on the condition
of material excavated during a single work cycle and automatically
selecting one of the plurality of control curves in response to the
determined material condition setting.
8. A method, as set forth in claim 7, including the steps of:
calculating a bucket payload value;
calculating the work performed by stick and bucket cylinders during
a digging portion of the work cycle; and
deriving a bucket payload/work quotient value by dividing the
bucket payload value by the work performed, the divisional result
being indicative of a condition of the material.
9. A method, as set forth in claim 8, including the steps of:
storing a plurality of predetermined bucket payload/work quotient
values corresponding to a plurality of predetermined material
condition values;
comparing the calculated bucket payload/work quotient value to the
stored bucket payload/work quotient values; and
selecting one of the plurality of control curves in response to the
comparison.
10. A method, as set forth in claim 7, including the steps of:
calculating a bucket payload value;
calculating the time elapsed during a single pass of the digging
portion of the work cycle; and
dividing the bucket payload value by the elapsed time to determine
a productivity value for the digging pass, the productivity value
being indicative of a condition of the material.
11. A method, as set forth in claim 10, including the steps of:
storing a plurality of predetermined productivity values
corresponding to a plurality of predetermined material condition
values;
comparing the calculated productivity value to the stored
productivity values; and
selecting one of the plurality of control curves in response to the
comparison.
12. A control system, as set forth in claim 7, including the steps
of:
calculating a bucket payload value; and
estimating a bucket fill percentage, said bucket fill percentage
being representative of the amount that the bucket is filled with
excavated material, said bucket fill percentage being function of
said bucket payload value and indicative of a condition of the
material.
13. A method, as set forth in claim 12, including the steps of:
storing a plurality of predetermined bucket fill values
corresponding to a plurality of predetermined material condition
values;
comparing the estimated bucket fill value to the stored bucket fill
values; and
selecting one of the plurality of control curves in response to the
comparison.
14. A method, as set forth in claim 7, including the steps of:
calculating a moment arm magnitude value, said moment arm magnitude
value being representative of the external force acting on the
bucket, said moment arm magnitude value being indicative of a
condition of the material.
15. A method, as set forth in claim 14, including the steps of:
storing a plurality of predetermined moment arm magnitude values
corresponding to a plurality of predetermined material condition
values;
comparing the calculated moment arm magnitude value to the stored
moment arm magnitude values; and
selecting one of the plurality of control curves in response to the
comparison.
16. A control system for automatically controlling a work implement
through a machine work cycle, said implement having a bucket
controllably actuated by at least one hydraulic cylinder,
comprising:
memory means for storing a plurality of command signal magnitudes
for controlling said at least one hydraulic cylinder, said command
signal magnitudes being described in correspondence with respective
hydraulic cylinder pressures by a plurality of control curves, each
control curve corresponding to a material condition setting that is
representative of a condition of an excavated material;
logic means for selecting one of the plurality of control curves
responsive to a determined said material condition setting
indicated by the condition of the excavated material and
responsively producing command signals having a magnitude dictated
by the selected said control curve; and
actuating means for receiving the command signals and responsively
actuating predetermined ones of the hydraulic cylinders to perform
the work cycle.
17. A control system, as set forth in claim 16, further comprising
said logic means determining said material condition setting based
on the condition of material excavated during a digging portion of
a work cycle and automatically selecting one of the plurality of
control curves to control a subsequent subsequent work cycle in
response to the determined material condition setting.
18. A control system, as set forth in claim 17, further comprising
said logic means:
calculating a bucket payload value; calculating a second value
representing at least one of the elapsed time and the work required
to excavate said material; and determining said material condition
on the basis of a ratio between said payload and said second
values.
19. A control system, as set forth in claim 17, further comprising
said logic means:
calculating a bucket payload value; and
estimating a bucket fill percentage, said bucket fill percentage
being representative of the amount that the bucket is filled with
excavated material, said bucket fill percentage being function of
said bucket payload value and indicative of a condition of the
material.
Description
TECHNICAL FIELD
This invention relates generally to the field of excavation and,
more particularly, to a self-adapting control system and method
that automates the excavation work cycle of an excavating
machine.
BACKGROUND ART
Work machines such as excavators, backhoes, front shovels, and the
like are used for excavation work. These excavating machines have
work implements which consist of boom, stick and bucket linkages.
The boom is pivotally attached to the excavating machine at one
end, and to its other end is pivotally attached a stick. The bucket
is pivotally attached to the free end of the stick. Each work
implement linkage is controllably actuated by at least one
hydraulic cylinder for movement in a vertical plane. An operator
typically manipulates the work implement to perform a sequence of
distinct functions which constitute a complete excavation work
cycle.
In a typical work cycle, the operator first positions the work
implement at a dig location, and lowers the work implement downward
until the bucket penetrates the soil. Then the operator executes a
digging stroke which brings the bucket toward the excavating
machine. The operator subsequently curls the bucket to capture the
soil. To dump the captured load the operator raises the work
implement, swings it transversely to a specified dump location, and
releases the soil by extending the stick and uncurling the bucket.
The work implement is then returned to the trench location to begin
the work cycle again. In the following discussion, the above
operations are referred to respectively as boom-down-into-ground,
dig-stroke, capture-load, swing-to-dump, dump-load, and
return-to-trench.
The earthmoving industry has an increasing desire to automate the
work cycle of an excavating machine for several reasons. Unlike a
human operator, an automated excavating machine remains
consistently productive regardless of environmental conditions and
prolonged work hours. The automated excavating machine is ideal for
applications where conditions are dangerous, unsuitable or
undesirable for humans. An automated machine also enables more
accurate excavation making up for the lack of operator skill.
The present invention is directed to overcoming one or more of the
problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention, a control system for
automatically controlling a work implement of an excavating machine
through a machine work cycle is disclosed. The work implement
including a boom, stick and bucket, each being controllably
actuated by at least one respective hydraulic cylinder. A plurality
of command signal magnitudes associated with at least one hydraulic
cylinder are stored. The command signal magnitudes are represented
by a plurality of control curves, where each control curve is
responsive to a material condition setting that is representative
of a predetermined condition of the excavating material. A
microprocessor selects one of the plurality of control curves and
responsively produces a command signal having a magnitude dictated
by the selected control curve. A electrohydraulic system receives
the command signal and controllably actuates predetermined ones of
the hydraulic cylinders to perform the work cycle.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, reference may
be made to the accompanying drawings in which:
FIGS. 1A,1B are a diagrammatic views of a work implement of an
excavating machine;
FIG. 2 is a hardware block diagram of a control system of the
excavating machine;
FIG. 3 is a top level flowchart representing the control of an
excavation work cycle;
FIG. 4 is a table representing control curves pertaining to a boom
cylinder command for a predig portion of the work cycle;
FIG. 5 is a table representing control curves pertaining to a boom
cylinder command for a digging portion of the work cycle;
FIG. 6 is a table representing control curves pertaining to a
bucket cylinder command for the digging portion of the work
cycle;
FIG. 7 is a table representing various setpoint values associated
with various portions of the work cycle;
FIG. 8 is a second level flowchart of an embodiment of a tuning
function;
FIG. 9 is a table representing a plurality of payload/work values
corresponding to a plurality of predetermined material condition
settings associated with the embodiment of FIG. 8;
FIG. 10 is a second level flowchart of another embodiment of the
tuning function;
FIG. 11 is a table representing a plurality of predetermined bucket
fill values corresponding to a plurality of predetermined material
condition settings associated with the embodiment of FIG. 10;
FIG. 12 is a second level flowchart of yet another embodiment of
the tuning function;
FIG. 13 is a table representing a plurality of productivity values
corresponding to a plurality of predetermined material condition
settings associated with the embodiment of FIG. 12;
FIG. 14 is a second level flowchart of another embodiment of the
tuning function;
FIG. 15 is a table representing a plurality of moment arm values
corresponding to a plurality of predetermined material condition
settings associated with the embodiment of FIG. 14;
FIGS. 16A, 16B, 16C are diagrammatic views of a work implement
illustrating the embodiment of FIG. 14;
FIG. 17 is a side view of the excavating machine; and
FIG. 18 is a diagrammatic view of the work implement during various
stages of the excavation work cycle.
BEST MODE FOR CARRYING OUT THE INVENTION
With reference to the drawings, FIG. 1 shows a planar view of a
work implement 100 of an excavating machine, which performs digging
or loading functions similar to that of an excavator, backhoe
loader, and front shovel.
The excavating machine may include an excavator, power shovel,
wheel loader or the like. The work implement 100 may include a boom
110 stick 115, and bucket 120. The boom 110, is pivotally mounted
on the excavating machine 105 by boom pivot pin 1. The center of
gravity of the boom (GBM) is represented by point 12. The stick 115
is pivotally connected to the free end of the boom 110 at stick
pivot pin 4. The center of gravity of the stick (GST) is
represented by point 13. The bucket 120 is pivotally attached to
the stick 115 at bucket pivot pin 8. The bucket 120 includes a
rounded portion 130, a floor designated by point 16, and a tip
designated by point 15. The center of gravity of the bucket (GBK)
is represented by point 14.
A horizontal reference axis, R, is defined having an origin at pin
1 extending through point 26. The axis, R, is used to measure the
relative angular relationship between the work vehicle 105 and the
various pins and points of the work implement 100.
The boom 110, stick 115 and bucket 120 are independently and
controllably actuated by linearly extendable hydraulic cylinders.
The boom 110 is actuated by at least one boom hydraulic cylinder
140 for upward and downward movements of the stick 115. The boom
hydraulic cylinder 140 is connected between the work machine 105
and the boom 110 at pins 11 and 2. The center of gravities of the
boom cylinder and cylinder rod are represented by points CG19,CG20,
respectively. The stick 115 is actuated by at least one stick
hydraulic cylinder 145 for longitudinal horizontal movements of the
bucket 120. The stick hydraulic cylinder 145 is connected between
the boom 110 and the stick 115 at pins 3 and 5. The center of
gravities of the stick cylinder and cylinder rod are represented by
points CG22,CG23, respectively. The bucket 120 is actuated by a
bucket hydraulic cylinder 150 and has a radial range of motion
about the bucket pivot pin 8. The bucket hydraulic cylinder 150 is
connected to the stick 115 at pin 6 and to a linkage 155 at pin 9.
The linkage 155 is connected to the stick 115 and the bucket 120 at
pins 7 and 10, respectively. The center of gravities of the bucket
cylinder and cylinder rod are represented by points CG25,CG26,
respectively. For the purpose of illustration, only one boom,
stick, and bucket hydraulic cylinder 140,145,150 is shown in FIG.
1.
To ensure an understanding of the operation of the work implement
100 and hydraulic cylinders 140,145,150 the following relationship
is observed. The boom 110 is raised by extending the boom cylinder
140 and lowered by retracting the same cylinder 140. Retracting the
stick hydraulic cylinders 145 moves the stick 115 away from the
excavating machine 105, and extending the stick hydraulic cylinders
145 moves the stick 115 toward the machine 105. Finally, the bucket
120 is rotated away from the excavating machine 105 when the bucket
hydraulic cylinder 150 is retracted, and rotated toward the machine
105 when the same cylinder 120 is extended.
Referring now to FIG. 2, a block diagram of an electrohydraulic
system 200 associated with the present invention is shown. A means
205 produces position signals in response to the position of the
work implement 100. The means 205 includes displacement sensors
210,215,220 that sense the amount of cylinder extension in the
boom, stick and bucket hydraulic cylinders 140,145,150
respectively. A radio frequency based sensor described in U.S. Pat.
No. 4,737,705 issued to Bitar et al. on Apr. 12, 1988 may be
used.
It is apparent that the work implement 100 position is also
derivable from the work implement joint angle measurements. An
alternative device for producing a work implement position signal
includes rotational angle sensors such as rotatory potentiometers,
for example, which measure the angles between the boom 110, stick
115 and bucket 120. The work implement position may be computed
from either the hydraulic cylinder extension measurements or the
joint angle measurement by trigonometric methods. Such techniques
for determining bucket position are well known in the art and may
be found in, for example, U.S. Pat. No. 3,997,071 issued to Teach
on Dec. 14, 1976 and U.S. Pat. No. 4,377,043 issued to Inui et al.
on Mar. 22, 1983.
A means 225 produces pressure signals in response to the force
exerted on the work implement 100. The means 225 includes pressure
sensors 230,235,240 which measure the hydraulic pressures in the
boom, stick, and bucket hydraulic cylinders 140,145,150
respectively. The pressure sensors 230,235,240 each produce signals
responsive to the pressures of the respective hydraulic cylinders
140,145,150. For example, cylinder pressure sensors 230,235,240
sense boom, stick and bucket hydraulic cylinder head and rod end
pressures, respectively. A suitable pressure sensor is provided by
Precise Sensors, Inc. of Monrovia, Calif. in their Series 555
Pressure Transducer, for example.
A swing angle sensor 243, such as a rotary potentiometer, located
at the work implement pivot point 180, produces an angle
measurement corresponding to the amount of work implement rotation
about the swing axis, Y, relative to the dig location.
The position and pressure signals are delivered to a signal
conditioner 245. The signal conditioner 245 provides conventional
signal excitation and filtering. A Vishay Signal Conditioning
Amplifier 2300 System manufactured by Measurements Group, Inc. of
Raleigh, N.C. may be used for such purposes, for example. The
conditioned position and pressure signals are delivered to a logic
means 250. The logic means 250 is a microprocessor based system
which utilizes arithmetic units to control process according to
software programs. Typically, the programs are stored in read-only
memory, random-access memory or the like. The programs are
discussed in relation to various flowcharts.
The logic means 250 includes inputs from two other sources:
multiple joystick control levers 255 and an operator interface 260.
The control lever 255 provides for manual control of the work
implement 100. The output of the control lever 255 determines the
work implement 100 movement direction and velocity.
A machine operator may enter excavation specifications such as
excavation depth and floor slope through an operator interface 260
device. The operator interface 260 may also display information
relating to the excavating machine payload. The interface 260
device may include a liquid crystal display screen with an
alphanumeric key pad. A touch sensitive screen implementation is
also suitable. Further, the operator interface 260 may also include
a plurality of dials and/or switches for the operator to make
various excavating condition settings.
The logic means 250 receives the position signals and responsively
determines the velocities of the boom 110, stick 115, and bucket
120 using well known differentiation techniques. It will be
apparent to those skilled in the art that separate velocity sensors
may be equally employed to determine the velocities of the boom,
stick and bucket.
The logic means 250 additionally determines the work implement
geometry and forces in response to the position and pressure signal
information.
For example, the logic means 250 receives the pressure signals and
computes boom, stick, and bucket cylinder forces, according to the
following formula:
where P.sub.2 and P.sub.1 are respective hydraulic pressures at the
head and rod ends of a particular cylinder 140,145,150, and A.sub.2
and A.sub.1 are cross-sectional areas at the respective ends.
The logic means 250 produces boom, stick and bucket cylinder
command signals for delivery to an actuating means 265 which
controllably moves the work implement 100. The actuating means 265
includes hydraulic control valves 270,275,280 that control the
hydraulic flow to the respective boom, stick and bucket hydraulic
cylinders 140,145,150. The actuating means 265 also includes a
hydraulic control valve 285 that controls the hydraulic flow to the
swing assembly 185.
Referring now to FIG. 3, a flow diagram of an automated excavation
work cycle is shown. The work cycle for an excavating machine 105
can generally be partitioned into six distinctive and sequential
functions: boom-down-into-ground 305, pre-dig 307, dig-stroke 310,
capture-load 315, dump-load 320, and return-to-dig 323. The
dump-load function 320 advantageously includes a tuning function
330.
The present invention includes several embodiments of the tuning
function 330. Therefore, only the tuning function 330 will be
discussed in detail, as the detail of the other functions are not
critical to the present invention. However, for greater discussion
of the other functions, the reader is referred to U.S. Pat. No.
5,446,980 issued on Sep. 5, 1995 and entitled "Automatic Excavation
Control System and Method", which was filed on the same date as the
present application and is hereby incorporated by reference.
The tuning function 330 selects a material condition setting
determinative of the appropriate ones of a plurality of control
curves that command the displacement of the boom, stick, and bucket
cylinders 140,145,150 at desired velocities. An example set of
control curves are shown in the tables of FIGS. 4-6. Each control
curve is representative of a command signal magnitude that controls
the displacement of the boom, stick, and bucket cylinders
140,145,150. The curves may be defined by two-dimensional look-up
tables or a set of equations that are stored in the microprocessor
memory. The controlling curve is responsive to a material condition
setting that represents the condition of the ground soil. For
example, at the extremes, material condition setting 1 represents a
loose condition of the material, while material condition setting 9
represents a hard packed condition of the material. Thus,
intermediate material conditions settings 2-8 represent a continuum
of material conditions from a loose or soft material condition to a
hard material condition. It will be understood by those skilled in
the art that the number of the control curves are responsive to the
desired characteristics of the control.
Although the control curves may be automatically selected by the
logic means 250, the operator interface 260 is provided to allow
the operator to select a material condition setting corresponding
to one or all the sets of the control curves. This gives the
overall control greater flexibility.
The tables are now described:
FIG. 4 represents a table that stores the control curves associated
with the boom cylinder 140 for pre-dig portion of the excavating
work cycle. The magnitude of the command signal is responsive to
the pressure or force imposed on the bucket cylinder 150.
FIG. 5 represents a table that stores the control curves associated
with the boom cylinder 140 for the digging portion of the
excavating work cycle. The magnitude of the command signal is
responsive to the pressure or force imposed on the stick cylinder
145.
FIG. 6 represents a table that stores the control curves associated
with the bucket cylinder 150 for the digging portion of the
excavating work cycle. The magnitude of the command signal is
responsive to the pressure or force imposed on the bucket cylinder
150. With each table, the controlling curve is responsive to the
material condition setting. Thus, the material condition setting is
important for efficient excavation performance.
The present invention selects the appropriate control curve in
response to estimating the actual condition of the material. The
forgoing technique is not only valuable in determining the
appropriate control curve but also may be valuable for determining
one of a plurality of excavation set points. For example, the
excavator control may compare cylinder displacements and pressures
to a plurality of set points during the excavation work cycle. FIG.
7 shows a table that stores a plurality of setpoints for stick and
bucket cylinder displacements, where each setpoint is responsive to
a material condition setting.
The tuning function 330 uses several force calculations on the
bucket 120 to estimate the material condition. These force
calculations will now be described. Reference is made to the
diagrammatic views of the work implement in FIGS. 1A and 1B. First,
the logic means 250 determines the work implement geometry relative
to the reference axis, R, in response to position information. The
relative location of predetermined ones of the pins, points and
center of gravities are calculated using well known geometric and
trigonometric laws. For example, the work implement geometry may be
determined by using the inverse trig functions, the law of sines
and cosines, and their inverses. Further, the various forces on
predetermined ones of the pins may be determined in response to
position and pressure information. For example, the location and
magnitude of the forces on the pins may be determined by using
two-dimensional vector cross and dot products. It should be noted
that the work implement geometry and force information may be
determined by several methods well understood by those skilled in
the art. For example, the various forces on the pins may be
directly measured by using strain gauges or other structural load
measurement methods.
Note, for the following description, the term "angle R.X.Y"
represents the angle in radians between a line parallel to the
reference axis, R, and the line defined by pins X and Y. The term
"length X.Y" represents the length between points X and Y.
First, the sum of the forces on the boom-stick-bucket in the
x-direction is determined in the following manner:
.epsilon. F.sub.x boom-stick-bucket=
where,
F.sub.x BUCKET is the external force applied to the bucket in the
x-direction;
F.sub.x pin 1 represents the force applied to pin 1 in the
x-direction, which may be determined by summing the forces on the
boom at pin 1; and
F.sub.x pin 2 represents the force applied to pin 2 in the
x-direction, which is due to the axial force in the boom
cylinder.
Rearranging equation (1) and solving for the force component,
F.sub.x BUCKET, equation (1) is simplified as:
F.sub.x BUCKET=-F.sub.x pin 1-(axial force in the boom
cylinder)*cos (angle R.11.2)
Second, the sum of the forces on the boom-stick-bucket in the
y-direction may be calculated in a similar manner.
.epsilon. F.sub.y boom-stick-bucket=
where,
F.sub.y BUCKET is the external force applied to the bucket in the
y-direction;
F.sub.y pin 1 represents the force applied to pin 1 in the
y-direction, which may be determined by summing the forces on the
boom at pin 1; and
F.sub.y pin 2 represents the force applied to pin 2 in the
y-direction, which is due to the axial force in the boom
cylinder.
Rearranging equation (2) and solving for the force component,
F.sub.y BUCKET, equation (2) is shown as:
F.sub.y BUCKET=-F.sub.y pin 1-(axial force in the boom
cylinder)*sin(angle R.11.2)+.epsilon. boom-stick-bucket weight+(the
stick and bucket cylinder and rod weights)+(boom cylinder and rod
weight at pin 2)
The external force applied to the bucket, F.sub.xy is calculated
according to:
F.sub.xy =.sqroot.[(F.sub.y BUCKET).sup.2 +(F.sub.x BUCKET).sup.2
]
Finally, the moment arm of the external force on the bucket,
MABUCKET, is calculated about pin 8 by summing the moments about
pin 8. First, the force on the bucket normal to line 8.15, F.sub.N
BUCKET, is calculated according to the following relationship:
##EQU1## To properly identify the quadrant where .alpha. resides,
adjustment may made to .alpha. based on positiveness or
negativeness of F.sub.x BUCKET and F.sub.y BUCKET. For example, if
F.sub.x BUCKET and F.sub.y BUCKET have both negative values, then H
radians are subtracted from .alpha.. Moreover if F.sub.x BUCKET has
a negative value, while F.sub.y BUCKET has a positive value, then H
radians are added to .alpha..
Second, the moment about pin 8, M.sub.8, is calculated according
to: ##EQU2## Finally, the moment arm of the external force on the
bucket, MA BUCKET, is calculated according to:
MA BUCKET=M.sub.8 /F.sub.N BUCKET
The tuning function 330 is now described. The tuning function 330
"tunes" the excavating performance by determining the appropriate
ones of the plurality of control curves used in FIGS. 4-6 or the
appropriate one of the plurality of material condition settings of
FIG. 7. The tuning function 330 determines the appropriate material
condition setting based on current operating conditions of the
excavation work cycle. FIGS. 8, 10, 12, and 14 are flowcharts
illustrating a program control for implementing the preferred
embodiment of the present invention.
One method of performing the tuning function 330 is described with
reference to the flowchart of FIG. 8. First, the payload carried in
the bucket 120 is determined at block 805. The payload may be
determined by well known methods. For example, based on the work
implement geometry and cylinder forces the payload may be
determined. One such payload determination is shown by Applicant's
co-pending application entitled "Payload Determining System For An
Excavating Machine" (Atty. Docket No. 93-327), which was filed on
the same date as the present application and is hereby incorporated
by reference. Next, at block 810, the work performed by the stick
and bucket cylinders 145,150 during the prior dig pass is
calculated. Preferably, the work calculations are made just after
each dig pass. The work may be calculated according to the
following formula:
The calculated payload value is then divided by the work value at
block 815. Finally, the result of block 815 is then compared to
values of a two-dimensional look-up table to determine the
appropriate material condition setting at block 820.
For example, reference is now make to FIG. 9, which represents a
table of a plurality of predetermined payload/work values that
correspond to a plurality of predetermined material conditions.
Here, the control matches the calculated payload/work value with
the values of the look-up table. If the current material condition
setting deviates from that shown by the look-up table for the
calculated payload/work value, then the current material condition
setting is set to that shown by the look-up table. Otherwise, the
material condition setting is unchanged.
This method shows that the harder the material, the greater amount
of work is required to excavate the material for a predetermined
amount of payload, than for a softer material. Thus, based on the
payload to work ratio, the appropriate material condition setting
may be determined.
Another method of performing the tuning function 330 is described
with reference to the flowchart of FIG. 10. First, the payload
carried in the bucket 120 is calculated at block 1005. Then, in
response to the payload calculation, the percent of maximum fill of
the bucket 120 is determined at block 1010. For example, based on
the bucket capacity, the payload calculation can give an estimation
of the percent of maximum fill of a typical earthen material that
is captured in the bucket 120. At block 1015, the above result is
compared to values of a two-dimensional look-up table to determine
if material condition setting is set to the appropriate value.
For example, reference is now make to FIG. 11, which represents a
table of a plurality of predetermined percent of maximum fill
values that correspond to a plurality of predetermined material
conditions. Here, the control compares the calculated percent of
fill value with the predetermined percent of fill values to
determine if the material condition setting is set to the
appropriate value. The table shows that a softer material will fill
the bucket with a greater amount of material than a harder
material. Thus, based on the calculated percent of maximum fill,
the material condition setting may be evaluated.
If the calculated percent of maximum fill falls within the range
established by the table for the current material condition
setting, then the material condition setting is said to be set to
the appropriate value. However, if the calculated percent of
maximum fill falls outside the range established by the table for
the current material condition setting, then the material condition
setting should be modified. For example, if the calculated percent
of maximum fill is 80% and the current material condition setting
is "5", then the material condition setting is appropriate.
However, if the current material condition setting is "9" rather
than "5", then the material condition setting should be
modified.
As indicated by block 1020, a set of rules may be used to determine
the appropriate material condition setting. An example set of rules
is shown below:
CURRENT MATERIAL CONDITION SETTING=1
1. If bucket fill is greater than 85% of max fill, then o.k.
2. If bucket fill is between 70% and 85%, then change material
condition setting to 3.
3. If bucket fill is between 50% and 70%, then change material
condition setting to 5.
4. If bucket fill is less than 50%, then change material condition
setting to 7.
CURRENT MATERIAL CONDITION SETTING=5
1. If bucket fill is greater than 90% of max fill, then change
material condition setting to 3.
2. If bucket fill is between 75% and 90%, then o.k.
3. If bucket fill is between 50% and 75%, then change material
condition setting to 7.
4. If bucket fill is less than 50%, then change material condition
setting to 9.
CURRENT MATERIAL CONDITION SETTING=9
1. If bucket fill is greater than 75%, then change material
condition setting to 5.
2. If bucket fill is between 62% and 75%, then change material
condition setting to 7.
3. If bucket fill is less than 62%, then o.k.
The above set of rules are for exemplary purposes only and does not
limit the present invention. It will be apparent to those skilled
in the art that a predetermined set of rules may be used to
determine the appropriate value for all material condition
settings.
Yet another method of performing the tuning function 330 is
described with reference to the flowchart of FIG. 12. First, the
payload carried in the bucket 120 is determined at block 1205.
Next, at block 1210, the time elapsed during the prior dig pass is
calculated. The time elapsed represents the time from start to
finish of a single dig-stroke operation. The calculated payload
value is then divided by the elapsed time, at block 1215, to
determine the efficiency or productivity of the work cycle. Then,
at block 1220, the productivity value is compared to values of a
two-dimensional look-up table to determine if the material
condition setting is set to the appropriate value.
For example, reference is now made to FIG. 13, which represents a
table of a plurality of predetermined productivity values that
corresponds to a plurality of predetermined material conditions.
Here, the control compares the calculated productivity value with
the predetermined productivity values for the current material
condition setting to determine if the material condition setting is
set to the appropriate value. The table shows that the softer the
material, the greater amount of productivity is yielded. Thus,
based on the calculated productivity, the material condition may be
evaluated.
If the calculated productivity value is within the range
established by the table of predetermined productivity values for
the current material condition setting, then the material condition
setting is said to be set to the proper value. However, if the
calculated productivity value falls outside the range established
by the table, then the material condition setting should be
modified. As shown by block 1225, the material condition setting
may be modified by a set of rules similar to that described above.
It is noted that determining a set of rules to modify the material
condition setting will readily be apparent to those skilled in the
art, based on the instant disclosure.
The final method of performing the tuning function 330 is described
with reference to the flowchart of FIG. 14. First, the moment arm,
MA BUCKET, is determined at block 1405 in accordance with the above
calculations. Next, at block 1410, the value of MA BUCKET is
divided by a predetermined value, L. The predetermined value, L,
represents a moment arm extending the entire distance from pin 8 to
the bucket tip, shown by FIG. 16A. At block 1415, the divisional
result is compared to values of a two-dimensional look-up table to
determine if the material condition setting is set to the
appropriate value.
For example, reference is now made to FIG. 15, which represents a
table of a plurality of predetermined values that corresponds to a
plurality of predetermined material conditions. Here, the control
compares the divisional result of block 1415 with the values of the
look-up table to determine if the material condition setting is set
to the proper value. The table shows that for a harder material the
external force on the bucket will be located closer to the bucket
tip, than for a softer material. Thus, based on the location of the
external force vector, the material condition may be evaluated.
If the calculated value is within the range established by the
table for the current material condition setting, then the material
condition setting is said to be set to the appropriate value.
However, if the calculated value falls outside the range
established by the table, then the material condition setting
should be modified. As shown by block 1420, the material condition
setting may be modified by a set of rules similar to that described
above.
FIGS. 16B,C show examples of the location of the external force
while the machine is excavating. FIG. 16B shows that the external
force is located near the tip of the bucket 120, which represents a
harder material. As shown in FIG. 16C, the external force is a
distance away from the bucket tip, which indicates that the
material is soft and is somewhat easy to excavate.
The methods described above may be used as discrete independent
methods or used in combination to supplement each other. Moreover,
it may be desirable to supplement the above methods with operator
selectability. For example, the material condition setting of the
control curves pertaining to the dig-stroke function, tables 5 and
6, may be manually set by the operator, while the remainder of the
material condition settings associated with the other tables may be
automatically set by the logic means 250. This allows for an
experienced operator to have greater control of the work cycle.
The values shown in the tables may be determined with routine
experimentation by those skilled in the art of vehicle dynamics,
and familiar with the excavation process. The values shown herein
are for exemplary purposes only.
Industrial Applicability
The operation of the present invention is best described in
relation to its use in relation to its use in earthmoving vehicles,
particularly those vehicles which perform digging or loading
functions such as excavators, backhoe loaders, and front shovels.
For example, a hydraulic excavator is shown in FIG. 17, where line
Y is a vertical line of reference.
In an embodiment of the present invention, the excavating machine
operator has at his disposal two work implement control levers and
a control panel or operator interface 260. Preferably, one lever
controls the boom 110 and bucket 115 movement, and the other lever
controls the stick 115 and swing movement. The operator interface
260 provides for operator selection of operator options and entry
of function specifications.
For an autonomous excavation operation, the operator is prompted
for a desired dig depth, dig location, and dump location. Reference
is now made to FIG. 18, which illustrates an excavation work cycle.
For this illustration, assume that the bucket 120 has entered the
ground. First, the logic means 250 initiates the pre-dig portion of
the work cycle 307 by commanding the bucket 120 to curl at nearly
full velocity until a predetermined cutting angle is reached. As
the bucket curls, the boom 110 is raised at a velocity dictated by
one of the control curves shown in FIG. 4. Simultaneously, the
stick 115 is commanded inward at a predetermined velocity. The
control curves dictate a command signal magnitude that produces a
predetermined amount of force in the bucket and stick cylinders
150,145 to produce a desired amount of penetration into the
ground.
Once the bucket 120 has curled to the predetermined cutting angle,
the logic means 250 initiates the dig-stroke portion of the work
cycle 310 by commanding the boom 110 to raise according to one of
the control curves of FIG. 5, while the bucket 120 is commanded to
curl according to one of the control curves of FIG. 6. The stick
115, however, is commanded at nearly full velocity to retrieve as
much material from the ground as possible. The control curves of
FIGS. 5 and 6 dictate command signal magnitudes that keep the stick
and bucket cylinder pressures at desirable levels.
Once the digging is complete, the logic means 250 initiates the
capture-load portion of the work cycle 315 by commanding the stick
velocity to reduce to zero, the boom 110 to raise, and the bucket
120 to curl.
Once the load is captured, the logic means 250 initiates the
dump-load portion of the work cycle 320 by commanding the work
implement 100 to rotate toward the dump location, the boom 110 to
raise, the stick 115 to reach, and the bucket 120 to uncurl, until
the desired dump location is reached. Additionally, the logic means
250 initiates the tuning portion of the work cycle 330 by
estimating the condition of the material and selecting a new
material condition setting, if necessary.
After the load is dumped, the logic means 250 initiates the return
to dig portion of the work cycle 323 by commanding the work
implement 100 to rotate toward the dig location, the boom 110 to
lower, and the stick 115 to reach a greater amount, until the dig
location is reached. Finally, logic means initiates the boom-down
portion of the work cycle 305 by commanding the boom 110 to lower
toward the ground until the bucket 120 makes contact with the
ground.
Other aspects, objects and advantages of the present invention can
be obtained from a study of the drawings, the disclosure and the
appended claims.
* * * * *